1. Field of the Invention
The present invention relates generally to alignment of contacts on an electronic device with corresponding electronic contacts of a corresponding circuit on a carrier substrate. More specifically, the present invention relates to the alignment of the discrete conductive elements of a ball grid array (BGA) type semiconductor device with terminal pads of a printed circuit board or other higher-level packaging. The inventive method and apparatus are particularly suitable for testing or low-volume production.
2. State of the Art
Surface mount technology employed in semiconductor device packaging has assisted in increasing integrated circuit density on a single carrier substrate while maintaining or even increasing functionality. In an effort to further increase integrated circuit density while improving functionality, semiconductor die size continues to decrease. As semiconductor packages decrease in size, various difficulties arise in the manufacture of the packaged semiconductor die as well as its assembly with carrier substrates such as printed circuit boards.
For example, a ball grid array (BGA) is a design of semiconductor device which includes an array of discrete conductive elements in the form of conductive balls, or bumps, disposed on a surface of the semiconductor device to be mounted to a carrier substrate. The array of discrete conductive elements is aligned with a mating array of conductive terminal pads formed on the carrier substrate, such as a printed circuit board. After proper alignment, the discrete conductive elements are electrically connected to the terminal pads. If the conductive elements comprise solder balls, this step typically includes a reflow process. However, in testing situations where only a temporary connection is required, simple contact of the conductive balls with the terminal pads may be sufficient. Proper alignment is crucial to effecting electrical contact. If the BGA device is misaligned with respect to the carrier substrate and terminal pads, one or more of the discrete conductive elements of the array may not make sufficient contact with the corresponding terminals pad(s). This, of course, may result in an inoperative circuit.
As BGA semiconductor devices are developed into smaller packages such as, for example, fine pitch BGAs, the size of the conductive balls is reduced. Likewise, the pitch, or the lateral spacing between adjacent conductive balls, also decreases. The reduction of ball size and pitch requires greater accuracy and tighter tolerances during manufacturing. Similarly, alignment of a BGA semiconductor device with the carrier substrate becomes increasingly difficult. Accurate alignment is conventionally accomplished with expensive, automated pick and place equipment which requires extensive programming.
Such automated pick and place equipment requires independent set up and programming depending on the type of semiconductor device being aligned and assembled. Various parameters are required for programming and operation, such as the size of the semiconductor device, location of the semiconductor device with respect to the carrier substrate and semiconductor device orientation with respect to the carrier substrate. Different alignment techniques may be employed depending on the type of semiconductor device as well. For example, alignment techniques may differ based on whether the device is a BGA, a thin small outline package (TSOP), a quad flat pack (QFP) or some other type of device. A TSOP, QFP and other similar semiconductor devices typically include conductive elements in the form of leads disposed around a portion or all of the periphery of the semiconductor device while a BGA semiconductor device, on the other hand, carries the discrete conductive elements on a major surface of a semiconductor die or interposer substrate. The ability to align a semiconductor device having visible leads, such as with a TSOP or QFP, may be accomplished using optical or sight techniques looking down on the device and carrier substrate from above. However, this ability is greatly diminished, if available at all, when aligning discrete conductive elements on a BGA semiconductor device with the corresponding, terminal-facing pads of a carrier substrate, since it would be necessary to view the array of discrete conductive elements and the terminal pads, retain such alignment in computer memory and then calculate correct alignment.
Alignment concerns are increased when the assembly or testing process is to be low-volume production. For example in rework, in various testing procedures, or in custom or small build projects, it is not always practical to expend the resources in programming and setting up automated equipment to assemble relatively few components. Thus, alignment may be performed partially or wholly as a manual operation. Manual alignment of such assemblies is difficult and time consuming at best, particularly when alignment is further complicated by an inability to utilize optical or sight alignment techniques.
Attempts to remedy such alignment difficulties have not proven to achieve complete success. For example, one solution to aligning a BGA semiconductor device with mating terminal pads of a carrier substrate has been to form mating cavities in a surface of the carrier substrate, wherein the terminal pads are formed in the mating cavities. Each individual cavity is configured to receive one of the discrete conductive elements of the BGA semiconductor device to effect self alignment of the semiconductor device. While such an approach attempts to remedy alignment difficulties where optical or sight processes are difficult if not impossible to employ, the described approach is problematic in that it relies on the accuracy of forming properly dimensioned and located discrete conductive elements on the BGA semiconductor device. Also, as with other techniques, it still fails to allow for visual or optical assistance in effecting or confirming alignment of discrete conductive elements of the semiconductor device with the carrier substrate.
In view of the shortcomings in the state of the art, it would be advantageous to provide a method of aligning BGA or other arrayed discrete conductive element-type semiconductor devices with corresponding carrier substrates or other higher-level packaging for attachment. Such attachment may be either permanent or temporary.
It would also be advantageous to provide a method of alignment, as well as an apparatus for performing such alignment which may be employed either manually or in conjunction with automated pick and place equipment. In the case of utilizing the method or apparatus in conjunction with automated equipment, it should be capable of easy implementation, without incurring excessive set up time or operational expense.